Method and apparatus for cable sensitizing

ABSTRACT

A method and apparatus for increasing the sensitivity of electric cable that contains a dielectric material that has been or will be polarized is disclosed. A cable containing a dielectric material that can be polarized is first polarized and then is slightly compressed in alternate planes 90* apart to increase the sensitivity of the cable. If the cable to be sensitized is already polarized, the sensitivity of the polarized cable can be increased by slightly compressing the cable with the apparatus of this invention which comprises at least two pair of rollers oriented 90* to each other.

United States Patent [191 Thompson Sept. 30, 1975 METHOD AND APPARATUS FOR CABLE SENSITIZING [75] Inventor: Herbert H. Thompson, Fairfax, Va.

[22] Filed: Aug. 15, 1974 [21] Appl. No.: 497,790

[56] References Cited 5 I UNITED STATES PATENTS 3/1878 Gilbert 72/235 9/1879 Lauth ..72 235 2/1881 Gearing ..72/235 6/1974 Baldy ..29/25.35

Prt'tttury E.\'amitterMilton S. Mehr Attorney, Agent, or F irm-Nathan Edelberg; Robert P. Gibson; Vincent W. Cleary [57] ABSTRACT A method and apparatus for increasing the sensitivity of electric cable that contains a dielectric material that has been'or will be polarized is disclosed. A cable containing a dielectric material that can be polarized is first polarized and then is slightly compressed in alternate planes 90 apart to increase the sensitivity of the cable. If the cable to be sensitized is already polarized, the sensitivity of the polarized cable can be increased by slightly compressing the cable with the apparatus of this invention which comprises at least two pair of rollers oriented 90 to each other.

3 Claims, 2 Drawing Figures iier US. Patant Sept. 30,1975

METHOD AND APPARATUS FOR CABLE SENSITIZING The invention described herein may be manufactured, used, and licensed by or for the Government for Governmental purposes without the payment to me of any royalties thereon.

BACKGROUND OF THE INVENTION This invention relates to sensitizing polarized electric cable, and more particularly to a method and apparatus for increasing the sensitivity of polarized electric cable.

Some electric cable contain a dielectric material that can be polarized. When a cable that has been polarized is subjected to mechanical stress, a potential difference can be measured between the inner and outer conductors of the cable. Unfortunately, the magnitude of such a potential difference is not necessarily consistent for the same type of cable even if the cable is purchased from the same manufacturer. This is true even though the polarizing process can be well defined and is repeatable. Therefore, it has not been possible to obtain a polarized cable that will consistently have a specific minimum output when stressed by a given amount. The prior art solution generally used to increase the sensitivity of polarized cable having a sensitivity below an acceptable level has been to repolarize the cable. Repolarization of the cable is a time consuming process and very often the repolarized cable still does not have an acceptable level of sensitivity.

This invention provides a method and the apparatus for increasing the sensitivity of cable polarized by a preferred method described herein and for increasing the sensitivity of cable polarized by the manufacturer. In accordance with this invention, the sensitivity of cable polarized by the manufacturer can be increased in a very short period of time without first going through the time consuming process of repolarization.

SUMMARY OF THE INVENTION In accordance with a preferred polarization method, a voltage is applied across the inner and outer conductors of cable containing a dielectric that can be polarized. The voltage is applied for at least a given period of time while the cable is maintained at an elevated temperature. The cable is then cooled at a specific cooling rate. After the cable has been cooled it is then processed through the sensitizing apparatus of this invention.

The sensitizing apparatus comprises two or more pair of rollers set and maintained so as to slightly compress the cable as it is passed between each pair of rollers. The axis of each successsive pair of rollers is positioned 90 to that of the preceeding pair, so that the cable is partially flattened in alternate planes 90 apart. By actual test, cables sensitized in accordance with this invention were found to have an increase in sensitivity of approximately 150% as compared to cables that were polarized but not processed through the sensitizing ap paratus of this invention.

The sensitizing apparatus of this invention can also be used to increase the sensitivity of cables polarized by the manufacturer. Prior to this invention, the practice has been to repolarize cable polarized by the manufacturer when the sensitivity of the cable is below an acceptable minimum level. This repolarizing process takes approximately three hours and is not always successful. With this invention the polarized cable is merely processed through the sensitizing apparatus of this invention. It takes approximately five minutes to process a fifty meter cable through the sensitizing apparatus of this invention. For test and evaluation purposes, cables polarized by the manufacturers were processed through the sensitizing apparatus of this invention and the sensitivity of each cable so processed was measured before and after the sensitizing. The results of these tests showed that the sensitivity of each cable processed was increased substantially above an acceptable minimum, even in those cases where the sensitivity of the cable was substantially below the acceptable minimum level.

BRIEF DESCRIPTION OF THE DRAWING A complete understanding of the objects and specific details of the invention can be obtained from the following detailed description when read in conjunction with the annexed drawing in which:

FIG. 1 shows the sensitizing rollers of this invention; and

FIG. 2 shows typical apparatus utilized to increase the sensitivity of a cable in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION The invention will first be described for the case where an unpolarized cable containing a dielectric material capable of being polarized is first polarized and then processed in accordance with this invention. The cable is first subjected to an elevated temperature by placing the cable in an oven, for example, or by any other suitable means. How the cable is heated is not significant. The important factor is that the temperature of the cable be raised to an appropriate level. The appropriate temperature level for a given cable is that temperature at which the dielectric material softens. This temperature is, of course, different for different materials. After the dielectric is softened, a voltage just below the breakdown voltage for the particular dielectric material of cable being processed is then applied across the inner and outer conductors of the cable while the cable is maintained at the elevated temperature. The cable is then cooled at a given rate while the voltage is maintained across the inner and outer conductors. The cooling rate is different for different dielectric materials. After the cable has cooled, the voltage is removed from the cable and the cable is now polarized.

As was mentioned, the time, temperature and voltage required is different for different dielectric materials. However, the required values of these parameters are well known for most, if not all, dielectric materials capable of being polarized. For example, the temperature at which a given dielectric material will become soft is known from the chemical make-up of the material, the breakdown voltage of a given cable is generally speci fied by the manufacturer, and data on the effect of temperature and heating and cooling rates on the polarization of a given dielectric material is available for most if not all such dielectric material. Of course, if such data as softening temperature, breakdown voltage and cooling rate for a given dielectric material is not available, such data can be obtained without a great deal of difficulty by known methods of experimentation. This of course is time consuming, but is not a very difficult task. Further, such data need only be collected one time for a given dielectric material.

After the cable has been polarized, it is now in condition for processing through the sensitizing apparatus of this invention. FIG. 1 shows the sensitizing device of this invention. This device will hereinafter be referred to as the sensitizer. As shown in FIG. 1, the sensitizer comprises an L-shaped frame 1 that carries a first pair of rollers 3 and a second pair of rollers 5. The axis of the first pair of rollers 3 is positioned 90 with respect to the axis of the second pair of rollers 5. The roller pairs 3 and are mounted to frame 1 by any suitable means that will permit each roller to freely rotate on its axis.

As is apparent from FIG. 1, a space or gap 2 exists between the two rollers of pair 3 and a space or gap 4 exists between the two rollers of pair 5. Gaps 2 and 4 are always equal. However, these gaps will be smaller or larger depending upon the size of the cable being processed for reasons that will become apparent later herein. It should be pointed out, however, that when the gaps 2 and 4 are set for a given cable size they are maintained at that setting until a different size cable is to be processed through the sensitizer.

FIG. 1 does not show any specific means for changing the gaps 2 and 4 since this can be accomplished in any one of several different but obvious ways. For example, separate sensitizers for each size cable with the gaps permanently set for each size cable could be provided. Instead of separate sensitizers for each size cable, different size rollers could be interchangeably mounted on frame 1. The smaller the rollers, the larger the gaps. Of course, gaps 2 and 4 could only be varied by given amount by using different size rollers. Thirdly, a plurality of mounting means or adjustable mounting means could be provided on frame 1 to adjust the gaps 2 and 4. Any size gap could be provided by having either adjustable mounting means or a plurality of separate mounting means on frame 1 by merely making frame 1 large enough to accommodate the largest gap desired. In addition to these three specific separate means for varying gaps 2 and 4, it is obvious that the three separate means could be combined in various combinations to provide further degrees of adjustment. For example, different size rollers could be used with adjustable means on frame 1 or a number of different sensitizers could be made with each sensitizer having adjustable means provided on the frame to accommodate different limited degrees of adjustment of the gaps. The various ways one could provide for adjusting the size of the gaps 2 and 4 are given merely to show that such adjustments can readily be accomplished and that how the adjustments are made is not significant to this invention. What is significant, as will be apparent later, is that gaps 2 and 4 are set to a given value for a particular cable and then maintained at that setting until a different size cable is processed. Frame 1 can be and would normally be mounted to a work surface such as a work bench or other surface by screws or other suitable means to hold the sensitizer in place.

The cable polarized as described above is processed through the sensitizer of FIG. 1 in the following manner: This cable is passed between the rollers of both roller pairs 3 and 5. The gaps 2 and 4 have been set such that the cable will be slightly flattened by the rollers. While the precise degree of this flattening is not critical, roller pairs 3 and 5 are set such that the cable isjust slightly flattened. Since roller pairs 3 and 5 are to each other, the cable will be flattened in two planes 90 apart. This flattening or compressing of the cable substantially increases the sensitivity of the polarized cable. By actual test, it has been found that the sensitivity of a cable polarized as described above and then processed through the sensitizer of FIG. 1 has been increased by approximately Various different cables have been processed through a sensitizer such as the sensitizer of FIG. 1 and in every case the increase in sensitivity has been approximately 150%.

The polarized cable can be processed through the roller pairs 3 and 5 of the sensitizers by hand; however, a more efficient and practical method is shown in FIG. 2.

FIG. 2 shows the sensitizer of FIG. 1 along with apparatus used to process the cable through the sensitizer. This apparatus comprises a first cable reel 9, a second cable reel 11, a motor 13 which may be an electric motor, and a power belt 14 coupling motor 13 to reel 13. In FIG. 2 the cable 7, which for the present is considered to be the cable polarized in the manner described above, is after polarization stored on reel 9. Reel 9 is detachably mounted on an axle 6 in such a manner that reel 9 is free to rotate. The free end of cable 7 is fed through the roller pairs 3 and 5 from reel 9 to take-up reel 11 by hand. In other words, cable 7 is first passed between rollers 5 and then between rollers 3 and then secured to reel 11. Reel 11 is detachably mounted on the axle 8 such that reel 11 will rotate when axle 8 is rotated. A pulley 10 is either formed in axle 8 or secured to axle 8. Motor 13 has a power pulley 12 which is driven by the motor. Belt 14 couples pulley 12 of motor 13 to pulley 10 of reel 11.

After cable 7 is passed between roller pairs 3 and 5 and secured to reel 11, motor 13 is energized. Motor 13 rotates reel 11 in the direction of the arrow on reel 11 to pay-out cable 7 from reel 9 and take-up cable 7 on reel 11 after it passes through rollers pairs 3 and 5.

The gaps of roller pairs 3 and 5 have been set to slightly flatten cable 7 in two planes separated by 90. Thus, the cable 7 taken up by reel 1 1 will have an increased sensitivity due to the flattening caused by roller pairs 3 and 5. With the apparatus of FIG. 2, a 50 meter long cable can be processed in about 5 minutes. The prior art repolarizing processes intended to increase the sensitivity of a polarized cable generally take approximately 3 hours and are not always successful. Thus, it is apparent that the sensitizing process of this invention is considerably less time consuming than the conventional repolarizing process and in addition the sensitizing process of this invention has, to date, always provided a polarized cable having a sensitivity substantially greater than the minimum acceptable value.

The sensitizer shown in FIG. 1, which is the same sensitizer shown in FIG. 2, has only two pair of rollers. If desired, additional pairs of rollers could be provided. If additional pairs of rollers are provided, frame 1 would of course have to be increased in size or additional frames would have to be provided. Where additional pairs of rollers are provided, the axis of each successive pair of rollers is positioned 90 to the axis of the preceding pair of rollers as is the case with roller pairs 3 and 5.

The sensitizing processes of this invention are not limited to cable polarized in the manner described above. The sensitivity of cable polarized by manufacturers can also be increased substantially by processing the cable through the sensitizer without first repolarizing the cable. Thus, cable 7 in FIG. 2 could be a cable polarized at the time of purchase. Reel 9 could be the reel supplied with the cable by the manufacturer provided that the manufacturers reel is of proper design to be detachably mounted on axle 6. This polarized cable is then merely processed through the sensitizer, after the gaps in the roller pairs are set, and taken up on reel 1 1. Again, by actual test, it has been shown that the sensitivity of a cable polarized by the manufacturer can be increased substantially above a minimum acceptable level by the sensitizer of this invention. However, it should be pointed out that the results obtained by first polarizing an unpolarized cable in the manner described herein and then processing the cable through the sensitizer have been, to a slight degree, superior to the results obtained by merely sensitizing a cable polarized by the manufacturer. This does not mean, however, that the sensitivity increase obtained by processing cable polarized by the manufactuer has not been satisfactory. The exact opposite is true. In all cases where cable polarized by the manufacturer has been processed through the sensitizer of this invention, the sensitivity of the cable has been increased substantially above a minimum acceptable level without first repolarizing the cable.

While the invention has been described as providing a method and apparatus for increasing the sensitivity of polarized cables per se, it has been found to be particularly suitable for increasing the sensitivity of audio-type cable. A specific audio cable that was processed through the sensitizer of this invention for test and evaluation purposes was an International Telephone and Telegraph teflon-shielded cable having a sixteen gauge center conductor. The test results showed a 150% increase in the sensitivity of the cable after it was processed through the sensitizer of this invention. This invention is not, however, limited to this specific cable nor to just audio-type cable.

From the foregoing description, it should be apparent that this invention provides a method and the apparatus for sensitizing polarizable cable or for sensitizing cable polarized at the time of manufacture. It should also be apparent to those skilled in the art that various modifications and changes can be made to the method and apparatus disclosed without departing from the spirit and scope of the invention as set forth in the claims.

I claim:

1. A method of changing the sensitivity of response of a polarized cable sensor means of the dielectric filled coaxial cable variety to external mechanical stress comprising the steps of:

a. subjecting said polarized cable sensor means of the dielectric filled coaxial cable variety to a slight compressive transverse force along the length thereof in a first selected plane and then b. subjecting said polarized cable sensor means to a slight compressive transverse force along the length thereof in a second selected plane substan- 'tially orthogonal to said first selected plane whereby the sensitivity of response of said sensor cable is increased.

2. The method as described in claim 1 wherein said sensor cable is subjected to slight compressive forces in orthogonal planes by pairs of compressive roller means as said sensor cable passes therethrough.

3. The method as described in claim 2 wherein said slight compressive forces are applied in substantially immediate successive order as said cable passes through said pairs of compressive roller means. 

1. A method of changing the sensitivity of response of a polarized cable sensor means of the dielectric filled coaxial cable variety to external mechanical stress comprising the steps of: a. subjecting said polarized cable sensor means of the dielectric filled coaxial cable variety to a slight compressive transverse force along the length thereof in a first selected plane and then b. subjecting said polarized cable sensor means to a slight compressive transverse force along the length thereof in a second selected plane substantially orthogonal to said first selected plane whereby the sensitivity of response of said sensor cable is increased.
 2. The method as described in claim 1 wherein said sensor cable is subjected to slight compressive forces in orthogonal planes by pairs of compressive roller means as said sensor cable passes therethrough.
 3. The method as described in claim 2 wherein said slight compressive forces are applied in substantially immediate successive order as said cable passes through said pairs of compressive roller means. 